1. Field of the Invention
The present invention generally relates to an apparatus for controlling fuel injectors of an internal combustion engine of cylinder injection type mounted on a motor vehicle. More particularly, the present invention is concerned with a fuel injector control apparatus for the cylinder injection type internal combustion engine which apparatus can ensure a failsafe function upon occurrence of a ground fault of a fuel injector.
2. Description of Related Art
In recent years, there has been developed and employed as the engine for motor vehicles a cylinder injection type internal combustion engine in which fuel injectors are installed on a cylinder-by-cylinder basis for directly injecting fuel into the cylinders at a high pressure in order to realize enhanced combustion efficiency.
In such cylinder injection type internal combustion engine, it is necessary not only to drive or actuate the fuel injectors at a high speed regardless of high pressure of the fuel but also to control the time duration of the fuel injection with a high accuracy.
To this end, the driving circuit for driving or actuating the fuel injector is so arranged that in an initial phase of injection valve opening operation, a high voltage is applied across an electromagnetic coil of the fuel injector for opening the injection valve, while after the injection valve has been opened, a constant current of a necessary minimum magnitude required for holding the injection valve in the opened state is fed for thereby preventing or suppressing generation of heat in the coil of the fuel injector. In reality, various types of injector driving circuits have heretofore been proposed in the art. For example, refer to Japanese Patent Application Laid-Open No. 318025/1998 (JP-A-1998-318025).
In the fuel injector driving/controlling apparatus disclosed in JP-A-1998-318025 mentioned above, the fuel supply quantity and the fuel injection timing for the engine are arithmetically determined on the basis of the information concerning the engine operation state derived from the outputs of various types of sensors, and the coils of the injectors provided on a cylinder-by-cylinder basis are electrically energized or excited from a battery onboard the motor vehicle. There are provided an injector driving circuit common to or shared by the fuel injectors of the first cylinder and the fourth cylinder on one hand and an injector driving circuit common to or shared by the fuel injectors of the second cylinder and the third cylinder on the other hand.
Further, there has been proposed an injector driving/controlling apparatus which differs in the circuit configuration from the apparatus disclosed in JP-A-1998-318025 in that a power supply circuit is shared by all the fuel injectors and which can thus be implemented at a lower manufacturing cost. Reference is to be made, for example, Japanese Patent No. 3336905.
Furthermore, there has been proposed an injector driving/controlling apparatus which is implemented in the circuit configuration similar to that disclosed in JP-A-1998-318025, and which apparatus is so arranged that upon detection of abnormality in an injector driving circuit, the fuel injections from all the fuel injectors sharing the injector driving circuit suffering the trouble is stopped, while the fuel injection to the cylinders which share in common the normally operating injector driving circuit is continued. For more particulars, reference may have to be made to, for example, Japanese Patent Application Laid-Open No. 112735/1997 (JP-A-1997-112735).
As is apparent from the above, in the injector driving circuits known heretofore, the power supply source for the driving circuits is partially shared by the fuel injectors on a per cylinder group basis to thereby realize inexpensive and miniaturized implementation of the driving circuits.
In this conjunction, it is however noted that with the circuit arrangement mentioned above, when a ground fault takes place at the grounded or earthed terminal of the electromagnetic coil of the fuel injector mounted on the first cylinder (e.g. when a wiring conductor extending between the electromagnetic coil of the fuel injector for the first cylinder and a switching means is electrically connected to the ground potential), the fuel injector for the first cylinder will nevertheless be driven simultaneously in synchronism with the fuel injector of the fourth cylinder which shares the driving circuit with the fuel injector of the first cylinder.
In this connection, it is assumed that the engine is of four-cylinder type, wherein the fuel is injected to the first, third, fourth and the second cylinders in this order. In that case, with the circuit configuration disclosed in JP-A-1998-318025 and in JP-A-1997-112735 in which one of the driving circuits is shared by the first and fourth cylinders, fuel injection to the first cylinder whose fuel injector suffers the ground fault is performed at the expansion stroke simultaneously with the fuel injection to the fourth cylinder performed at the suction stroke.
On the other hand, with the circuit configuration disclosed in Japanese Patent No. 3336905 in which the driving circuit is shared by the fuel injectors of all the cylinders, fuel injection to the first cylinder suffering the ground fault will always be carried out simultaneously with the driving of the fuel injectors for the second to fourth cylinders, respectively.
Furthermore, there has been proposed an apparatus designed for detecting an OFF surge voltage which makes appearance upon firing the injector coil (i.e., when electrical energization of the injector coil is interrupted or broken) for thereby detecting the wire breakage fault and the ground fault of the injector circuits en bloc. Refer to, for example, Japanese Patent Application Laid-Open No. 290111/1987 (JP-A-1987-290111). In this publication, however, no teaching is disclosed concerning the discriminative detection or identification of the wire breakage fault and the ground fault from each other.
In the apparatus described above, when the wire breakage fault takes place in the fuel injector for the first cylinder, no fuel injection is performed to the first cylinder. In that case, since the OFF surge signal drops out in relation to the first cylinder, it can be detected that the fuel injector of the first cylinder suffers abnormality.
On the other hand, in the case where the ground fault occurs in relation to the first cylinder, fuel injection to the first cylinder is carried out at the normal fuel injection timing and simultaneously in synchronism with the fuel injection timing for the fourth cylinder whose fuel injector shares the driving circuit with that of the first cylinder. In that case, although the driving switching means provided in association with the fuel injector of the first cylinder is in the off-state (i.e., turned off), the coil of the fuel injector of the first cylinder is electrically energized through the grounded location, as a result of which only the OFF surge signal for the first cylinder drops out similarly to the case where the wire breakage fault occurs as mentioned just above. In other words, although the fuel injection mode differs for the wire breakage fault and the ground fault, it can not discriminatively be identified which of the wire breakage fault and the ground fault has taken place with only the detection of the OFF surge voltage. Of course, for identifying the wire breakage fault and the ground fault discriminatively from each other, it is conceivable to provide additionally a detection circuit dedicated to this end. However, it will incur increase of the manufacturing cost, to disadvantage.
Next, let's consider a relation between the injector driving pulse and the current in the normal or ordinary operation state and the ground fault suffering state.
In the normal operation state, a high voltage is applied across the coil of the fuel injector in the initial phase of the injection valve opening operation for effectuating the injection valve opening operation at a high speed. Consequently, a large current will flow through the injector coil immediately after application of the injector driving pulse. However, after the injection valve has been opened, the hold current of a necessary minimum magnitude is caused to flow through the injector coil for holding the injection valve in the opened state while suppressing the heat generation.
On the other hand, upon occurrence of the short circuit fault, a major portion of the current flows to the injector coil, bypassing the switching means inserted between one end of the injector coil and the ground potential. Consequently, loss otherwise brought about by the switching means makes disappearance. Thus, the hold current of not a small magnitude will flow in addition to the large current flow in the initial phase of the valve opening operation, incurring increase of the heat quantity generated by the injector coil.
As is obvious from the foregoing, the injector control apparatuses for the cylinder injection type internal combustion engine known heretofore suffer a problem that the quantity of heat generated by the fuel injector increases upon occurrence of the short circuit fault.
Further, in the conventional apparatus adopting such circuit arrangement that the hold current is maintained constant through a feedback control effectuated on the basis of detection of the current flowing through the switching means, the hold current increases appreciably upon occurrence of the short circuit fault, as a result of which heat generation in the injector coil increases remarkably, incurring trouble or fault of the fuel injector and the driving circuit, giving rise to another problem.
Besides, in the case where the simultaneous fuel injection is continued, temperature of exhaust gas of the engine will increase because of the so-called after-burning, possibly incurring performance degradation of a catalyst disposed within the exhaust pipe of the engine. Moreover, because a large amount of unburned gas flows into the exhaust pipe, there may arise a possibility of spontaneous combustion of the unburned gas internally of the exhaust pipe, to a further problem.
Under the circumstances, there has been proposed the injector control apparatus for the cylinder injection type engine which is imparted with a failsafe function such that upon detection of the wire breakage fault and/or the ground fault, not only the fuel injection of the injector suffering the fault but also the fuel injection from all the other fuel injectors belonging to a same group as the fault suffering injector and sharing the driving circuit with the fault suffering injector is stopped while allowing the fuel injection from the normal injectors belonging to other group to be continued. In that case, since the fuel injection from the first cylinder (cylinder suffering the abnormality) and the fourth cylinder (normal cylinder), i.e., two cylinders in total, which share one driving circuit is stopped, the simultaneous fuel injection can certainly be avoided. However, since siding operation of the motor vehicle (i.e., operation for moving the motor vehicle to a safety zone such as a side area of a road) must then forcibly be carried out only with the two remaining cylinders (second and third cylinders), a half of the total cylinders, there may arise the possibility that engine torque as demanded can not be ensured, leading to engine stall in the worst case, to a further disadvantage.